Understanding Atmospheric Boundaries

International “DynVar” workshop focuses on the climate-relevant connections between the troposphere and stratosphere

Atmospheric researchers haven’t always crossed boundaries fluidly. There were those who focused on the troposphere, the layer of air down near Earth’s surface, where most of our weather phenomena occur and which has been warming. And those whose sights were set higher, in the stratosphere, where ozone depletion has been among the main events in recent decades.

Increasingly, however, scientists understand that the connections between the troposphere and stratosphere are critical for understanding past climate changes, for forecasting seasonal climate and for projecting the future.

About 70 researchers from around the world gathered at NOAA’s Earth System Research Laboratory in Boulder, CO in early November, for the second Dynamics and Variability (DynVar) of the Stratosphere-Troposphere System. The workshop, which concentrated on modeling, was organized by ESRL’s Judith Perlwitz (also with the Cooperative Institute for Research in Environmental Sciences) and colleagues from the United States, Germany, and the UK.ESRL’s Susan Solomon gave a keynote address suggesting that the audience members should look into the stratosphere. “I recommend investing yourself in stratospheric processes and their roles in climate,” Solomon said. “This is an amazing time to be working on the stratosphere.”

Researchers presented initial results or described experiments planned to clarify the relationship of the stratosphere to storm tracks, sea ice extent and circulation patterns such as El Niño-Southern Oscillation and North Atlantic Oscillation.

“We want to focus on the impact of the two-way stratosphere-troposphere coupling on mean climate, variability, and change,” Elisa Manzini (Max Planck Institute for Meteorology, Hamburg) said during an introduction to the workshop, which lasted three days.

Solomon drew upon some of her own recent research, which demonstrated that stratospheric changes in water vapor can help explain recent temperature changes at Earth’s surface.

Several speakers discussed now well-known work showing that the seasonal loss of stratospheric ozone in the Antarctic has amplified certain wind patterns, keeping the interior of the continent cold. In the future, ozone recovery, models show, will likely amplify Antarctic warming caused by the increase of greenhouse gases.

And many speakers looked to the future, describing planned modeling experiments to extract the roles of the stratosphere on climate. Seasonal Forecast Models and Earth System Models are beginning to go “high-top,” meaning they stretch high enough in altitude to account for stratospheric dynamics.

DynVar participants agreed that careful comparisons of “high-top” and comparable “low-top” models will be essential for determining whether including stratospheric processes will improve climate forecasts, from seasonal to decadal time scales.

“If you want to predict regional rainfall changes you need extended models” said Makoto Deushi, who discussed “The role of stratospheric ozone on the medium-range weather forecast.” Deuishi suggested that the DynVar group gathered in Boulder should lay plans for a careful, multi-model comparison of high-top vs. low-top model results available through the Coupled Model Intercomparison Project (CMIP5). CMIP5 data include the results of climate models run in support of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report, expected in 2013-2014.

The DynVAR 2 workshop was sponsored by NOAA’s Modeling, Analysis, Prediction and Projection (MAPP) Program, Stratospheric Processes and their Role in Climate (a core program of the World Climate Research Program), and the European integrating project COMBINE (Comprehensive Modelling of the Earth System for Better Climate Prediction and Projection).